Generaly this router should only have one port open, port 80.
But there is also the port 32764. So I googled and didnt found anything
usefull about it neither about the port in context of the router nor
about the port in generally.

nc gives me the following data in plaintext:
MMcS▒▒▒▒

In Hex its:
4d4d6353ffffffff

It first needs a challenge and then returns these strange string. I know
from nmap its an embedded linux 2.4.9 - 2.4.18 but that doesnt help me
anyways.

I seriously dont know what to do with it and how to handle this. The
vendor doesnt give me any information about that.

Does anyone knows something more or has an idea for me how to proceede?